7 Ways Your Body Betrays You

"Your brain is constantly generating expectations about the world and sending it back to the sensory system, so you interpret it in light of your expectations," said Alexandre Pouget, a cognitive neuroscience researcher at the University of Geneva.

So, if you're walking around the block and someone is walking toward you, your brain starts calculating the probability of who it's likely to be. That's why you'll think it's your next-door neighbor instead of a friend from another town. And most of the time, you'll be right: "It's counter-intuitive, but it's a smart strategy," Pouget said. "You'd think that you look at a face to figure out the identity of a person, but in fact the brain predicts the probability of who it's likeliest to be mathematically."

You can see how our expectations affect us in optical illusions as well. Take the classic Ponzo Illusion: two lines on a road or railroad track. Because we perceive one as being farther away, we see it as bigger when a ruler proves they are actually the same length.

Losing weight should be a simple formula: Calories in vs. calories out. But our brains muddle things up, neuroscientist and author Sandra Aamodt said in a TED talk.

The body has a set point, controlled by the brain, of what it thinks you should weigh. The set point has a range of about 15 pounds, and your body works hard to stay in that range, using chemical messengers from the hypothalamus gland to help regulate hunger, activity and metabolism.

Try to change that set point through diet, Aamodt says, and you'll likely fail. Instead, she says that health can be more readily achieved through intuitive eating (eating when you're hungry). While that may not be helpful if you're trying to squeeze into size 0 jeans, Aamodt said that intuitive eaters are often healthier.

We often think of our memories as factual videos. But some researchers think that every time we access a memory, it's subject to distortion.

"When you retell it, the memory becomes plastic, and whatever is present around you in the environment can interfere with the original content of the memory," Oliver Hardt, now a University of Edinburgh Centre for Cognitive and Neural Systems researcher, told Smithsonian.

That helps explain why almost 200 convicts have been exonerated through DNA evidence after eyewitnesses helped imprison them.

After a cross-country flight, a woman turned to her husband and said, "That was beautiful music they were playing on the airplane." Her husband looked at her and said, "No, there was no music." She didn't believe him until their return flight, when she again heard the music. It wasn't until he put his hearing aids in that she realized the music was in her head.

Neil Bauman, director of Center for Healing Loss Help, calls it Musical Ear Syndrome, and he's documented more than 1,500 cases of it. He explains it like this: Think of your brain as a system of highways. Cars usually stay on the right highways, but occasionally, one will sneak across. If a "car," or sound, from your memory routes itself onto the auditory highway, then the brain perceives it as coming from your ears -- in other words, it treats it as real.

It's so often misdiagnosed, though, that many people -- and sometimes their doctors -- believe they are simply going crazy.

"Very few doctors know anything about it," Bauman said. "Doctors may laugh at patients, or put them on psychiatric drugs. They're often not getting sensitive treatment."

Ruling out a brain tumor or other cause can ease people's fear, and Bauman's hope is that the more people learn about it, the more the stigma will get erased.

It's the visual equivalent of musical ear syndrome, Bauman said. These visual hallucinations most commonly affect people at the beginning of vision loss.

"The brain is starved for sight," Bauman said. "So people will say that they see a farm landscape on a wall, for example, or shapes or patterns."

Like musical ear syndrome, it can be scary because people think it's the sign of a mental health problem. Actually, researchers think it's your brain filling in gaps from loss of eyesight with stored visions.

Most people with spinal cord injuries experience terrible phantom limb pain, Allan Basbaum, chair of the anatomy department at University of California, San Francisco, and former editor of PAIN, the Journal of the International Association for the Study of Pain, told Discovery News.

The pain, which is perceived as originating from the missing limb, was once assumed to be a psychological problem, but experts now blame the spinal cord and brain. The nerves that used to send signals to the missing limb instead cause pain, which can vary from person to person.

"The experience of pain is in the brain," Basbaum said. "Just because there's no input doesn't mean that brain doesn't have a representation."

While it's rare, alien hand syndrome is very real -- and, once again, stems from the brain. The condition, which can be triggered by neurodegenerative disorders, tumors, or strokes, comes from a disconnect between the brain's signals that control the hand and those that recognize what it's doing.

While it sounds like something out of a movie, a patient's hand may grab things or fiddle with things against the patient's will.